The rubber compositions of the individual components of vehicle tires, in particular the composition of the tread, determine the traveling properties thereof to a high degree. For the purposes of the present text, the term vehicle tires encompasses pneumatic vehicle tires, solid rubber tires and two-wheel tires.
To influence the mixing and vulcanization properties, a very wide variety of additives are mixed into the mixtures and/or specific polymers are used. As additives, mention may be made by way of example at this point of fillers (for example, carbon black), plasticizers, aging inhibitors and crosslinking systems composed of sulfur, accelerator and activator.
Crosslinking of the polymer chains by means of the vulcanization system produces a three-dimensional wide-meshed chemical network, as a result of which the rubber mixture becomes, depending on the crosslinking density, for example harder and more resistant to cracking, in particular because of an increased tear propagation resistance.
Crosslinking results in formation of network nodes at which the polymer chains are linked to one another, usually via bridges, for example, sulfur bridges in the case of sulfur crosslinking of diene rubbers. The length of the sulfur bridges, that is, the number of S atoms per crosslinking bridge, depends on the ratio of sulfur to accelerator, with a distinction generally being made between a conventional network (sulfur/accelerator ratio of from 10:1 to 2:1), a semiefficient network (sulfur/accelerator ratio of from 2:1 to 1:2) and an efficient network (sulfur/accelerator ratio of from 1:2 to 1:10).
In sulfur crosslinking, the polymer chains are linked to one another via sulfur bridges in such a way that many free chain ends are present. These free polymer chain ends are particularly mobile and can absorb energy and convert it into kinetic energy. The rubber mixture therefore acts in an energy-damping manner, which has an adverse effect on the rolling resistance when used, for example, in vehicle tires.